Our invention relates to a message preamble detector, and particularly to a message preamble detector for providing an output signal after the preamble has been present for a selected time.
In radio and other types of electrical communication, binary signals are used to indicate information or to make an inquiry. For example, in a radio communication system, one station (such as a fixed station) may wish to know the status or condition of a second station (such as a mobile station). While the operator of the one station can make this inquiry by voice, such a procedure takes time, and if the operator of the second station is busy or absent, such a procedure is inefficient, or in some cases useless. For these and other reasons, binary systems have been provided to send predetermined messages or inquiries, and to send responsive replies. As persons familiar with this field know all too well, transmitted binary messages, inquiries, and replies are relatively susceptible to noise in any communication path, and are very susceptible to noise and fading if the communication path uses radio. In order that the binary messages, inquiries, and replies can be sent as reliably as possible, they are usually provided with a preamble to alert the receiving apparatus when a synchronizing word is to follow. With such an indication, the receiving apparatus will be synchronized with the transmitting apparatus so that the binary message will be accurately received.
Accordingly, a primary object of our invention is to provide a new and improved message preamble detector.
Another object of our invention is to provide a new and improved message preamble detector that is less susceptible to noise and fading on the communication path carrying the message.